1. Field of the Invention
The present invention relates to a head supporting structure for use in a disk drive system for double sided flexible disks. More particularly, the present invention pertains to a supporting structure for a dual magnetic head utilized for writing and reading data on a flexible disk which is a disk-shaped magnetic recording medium used in office automation equipment, for example, computers, word processors and so forth.
2. Description of the Related Art
Several different types of head supporting structure of the kind described above have heretofore been known. A critical consideration lies in how to allow the read/write (R/W) head to follow faithfully the surface of the flexible magnetic disk when rotating. A typical prior art will be described hereinunder.
The specification of U.S. Pat. No. 4,089,029 (first prior art) discloses a head supporting structure for the "0"-side of a flexible disk (hereinafter referred to as a "medium") as well as a head supporting structure for the "1"-side of the medium. The head supporting structure for the "0"-side and that for the "1"-side have the same structure except for the location of the head core for the "0"-side and that for the "1"-side.
More specifically, the head for the "0"-side and that for the "1"-side are supported by respective cantilever spring gimbals. The proximal portion of the "0"-side centilever spring gimbal and that of the "1"-side cantilever spring gimbal are fixed to respective arms which face each other across the medium. The heads are moved in contact with both sides of the medium, thereby magnetically writing or reading data on the medium.
According to the head supporting structure shown in the first prior art, both the cantilever spring gimbals are considerably flexible and therefore capable of following a relatively slight wobbling motion or a slight circumferential or radial distortion of the medium. The prior art is also capable of reducing the head load force (i.e., the force of contact of the head with the medium).
However, the prior art has the problems that, if the wobbling of the head is relatively large due to excessive warps or undulations of the medium, or if positioning of the medium relative to the head is inaccurate, the head is offset in the radial direction of the medium, resulting in inferior recording contact between the head and the medium.
The specification of U.S. Pat. No. 4,151,573 (second prior art) discloses an arrangement in which a carriage is installed at the "0"-side of a medium so as to be movable in the radial direction of the medium, and a button-shaped head is fixed to the carriage in such a manner that the buttonshaped head is in contact with the medium. Another head is disposed so as to be movable in contact with the "1"-side of the medium. The head is fixed on a cantilever spring gimbal which is held on the distal end of an arm. One end of the arm is hinged to the proximal end portion of the carriage. The head has a projection projecting from the center of its back, the projection being pressed by a pivot fixed on the arm. The force applied to the pivot is generated by pressing the whole of the arm with a coil spring.
The head supporting structure according to the second prior art has the advantages that the structure is simple and, since the head which is in contact with the "0"-side of the medium is fixed directly on the carriage, there is no fear of the head core being displaced in the radial direction of the disk. Accordingly, it is easy to set the position of the head in the radial direction of the disk and there is no fear of the head position being radially displaced due to warps or undulations of the disk.
However, in the structure according to the second prior art, the required recording contact is ensured by pressing the "1"-side head against the "0"-side head, and therefore, a comparatively high loading pressure is required to force a warped or undulated medium to come into good recording contact with the flat surface of the head for the "0"-side. Since the medium is distorted by this loading pressure, allowable loading pressure is limited. Accordingly, when the medium has excessive warps or undulations, a sligh gap may occur between the medium and the head surface even if the greatest allowable loading pressure (e.g., 20 to 25 g in the case of an ordinary head) is applied to the head.
Further, when the accuracy of the position of the head with respect to the medium is not sufficient, a gap can easily occur at the magnetic core gap position on the surface of the head which is in contact with the "0"-side of the medium. If the gap exceeds 0.2-0.3 .mu.m for a medium having an ordinary recording density, recording or reproduction of data cannot be effected satisfactorily. Accordingly, in order to obtain a higher recording density for a larger capacity, the gap between the head and the medium must be reduced in inverse proportion to the increase in the recording density. For this reason, this type of head supporting structure is not suitable for high density recording.
Japanese Utility Model Public Disclosure No. 55-7140 (third prior art) discloses an arrangement in which heads are disposed so as to face both sides, respectively, of a medium. The two heads have substantially the same head supporting structure in which each head is fixed on the center of a planar spring gimbal. The feature of this prior art resides in that no particular support point is needed for the back of the head and loading force applied to the medium is generated solely by the vertical deflection of the spring gimbal. Accordingly, in this case, even if the head wobbles vertically, there is no change in the position and posture of the head core in the direction of motion of the medium unless the posture of the mounting arm changes. Since the head has appropriate flexibility in the vertical direction and is pivotal about two axes, that is, an axis parallel to the direction of motion of the medium and an axis parallel to the radial direction of the medium, it is possible to achieve a considerably good recording contact between the medium and the head and also good follow-up of the head.
However, unlike the above-described second prior art, this head supporting structure allows the head to follow warps or undulations of the medium and hence tilt or rotate (rock) about an axis parallel to the direction of motion of the medium, so that the head core gap may be dynamically dislocated slightly in the radial direction of the medium. The slight dislocation of the head core gap occurs because the head slider, which is more than 2 mm in height, is tilted about the back of the gimbal. It should be noted that, since the medium is generally accommodated in a jacket or a casing, it is difficult to further reduce the space between the gimbal and the medium surface.
The above-mentioned dynamic movement of the head core in the radial direction of the medium causes a dislocation of the head, i.e., off-tracking. As a result, severe allowance is posed on the track margin. This allowance is particularly severe in the case of a disk driving apparatus for a high density recording in which the recording density in the track radial direction [a number of tracks per inch (TPI) or a number of tracks per millimeter (TPM)] is high.
Further, in a disk driving apparatus for high density and high capacity flexible disks in which a servo tracking technology is employed, a problem occurs in the follow up control when the dynamic off-tracking is too rapid, i.e., when the off-tracking occurs at high frequency.
Japanese Patent Publication No. 58-43828 (fourth prior art) discloses an arrangement in which heads which are movable in contact with the medium are fixed at the respective centers of gimbals. One of the gimbals is supported at its reverse side by two support points which are spaced radially of the medium. Each head is pivotal only about an axis parallel to a radius of the medium. In this case, even if the medium is warped or undulated, good circumferential follow-up of the heads can be achieved. In the radial direction, the heads are not allowed to swing, thereby preventing the occurrence of dynamic off-tracking.
This structure allows only a swing motion of the heads around an axis parallel to a radius of the medium, and substantially no swing motion around an axis parallel to the circumferential direction of the medium nor wobbling in the direction normal to the medium surface is allowed. Therefore, a gap may occur between the head core and the medium when, for example, the relative height of the medium and the head changes, in the same way as in the foregoing second prior art.
To overcome the above-described problems of the prior arts, the present applicant has already proposed a novel head supporting structure in U.S. Pat. Ser. No. 07/071,418, now U.S. Pat. No. 4,807,070. The present invention is an improvement in the head supporting structure proposed by the present applicant.